The instrument that Abby built for MusiCorps is based on a real instrument used by the band's percussionist.

NCIS writer Gina Lucita Monreal shared her take on the episode's end.

"Watching the MusiCorps Wounded Warrior band perform was an unforgettable experience," Monreal said. "We had 30 minutes of footage of them playing 'Hallelujah,' which we had to cut down to a three-minute montage."

The NCIS writers have a big message for all of the fans!

"Thanks to all our dedicated fans for helping us reach 300 episodes," they wrote. "We are so very grateful."